1. Field of the Invention
The present invention relates to an image recording apparatus, an image recording method, and a computer-readable recording medium, and more particularly to an image recording apparatus, an image recording method, and a computer-readable recording medium for controlling illumination amount when photographing with illumination.
2. Description of the Related Art
A flash illumination apparatus using a discharge tube (hereinafter also referred to as “strobe”) is commonly used as an illumination apparatus for a still camera. Such illumination apparatus operates by raising battery voltage and accumulating charge in a condenser having a relatively large capacity and instantly discharging the charge from a discharge tube having xenon sealed therein. Such illumination apparatus is widely used in still cameras from high class still cameras to popular still cameras owing to the fact that the illumination camera is i) suitable for recording still images by emitting a large amount of light and illuminating for an extremely short time (e.g., 1 ms), ii) illumination amount can be controlled with a relatively simple structured circuit owing to development of semiconductor switching devices, and iii) the illumination apparatus can be fabricated with a small size. In order to realize a suitable exposure with the strobe, it is necessary to control the illumination amount of the strobe. As one example of controlling the illumination amount, there is a flashmatic method. In the flashmatic method, the illumination amount necessary for realizing suitable exposure is expressed by the value of a guide number (GNo.) which is obtained by the following formula.GNo.=F×L wherein “F” indicates an F number of the photograph lens and “L” indicates the distance to the photograph target (in a case where the ISO sensitivity (ISO speed) of the film or the ISO equivalent sensitivity of the imaging device is 100).
As another example of controlling the illumination amount, there is an auto-strobe method. In the auto-strobe method, the light reflected from a target object in response to light emitted from the strobe is measured by using a photometric sensor mounted on a camera body or provided in a strobe mountable on a camera, to thereby stop illumination of the strobe when the value (measured value) output from the photometric sensor becomes a predetermined value (i.e. when reaching a suitable exposure state).
As another example of controlling the illumination amount, there is a TTL direct metering method. In the TTL direct metering method, the light reflected from a target object in response to light emitted from the strobe and reflected from a film surface via a photograph lens is measured by using a photometric sensor (light measuring sensor) mounted on a main body of a camera, to thereby stop illumination of the strobe when the value (measured value) output from the photometric sensor becomes a predetermined value (i.e. when becoming suitable exposure state).
As another example of controlling the illumination amount, there is a pre-illumination method. In the pre-illumination method, when a release switch is activated, a small amount of light is emitted from the strobe prior to a main photographing process (pre-illumination) for allowing a photometric sensor (or an imaging device in a case where the image device performs photoelectric conversion) mounted to a main body of a camera to measure the light reflected from a target object in response to the pre-illumination light. Accordingly, the illumination amount of the strobe for the main photographing process is determined based on the measurement results.
As another example of controlling the illumination amount, there is a method of determining the illumination amount of the strobe based on the distance obtained by calculating the distance to the target object according to the amount in which the focus lens veers out (See, for example, Japanese Laid-Open Patent Application No. 2002-311481).
However, the above-described auto-strobe method or the TTL direct metering method requires a photometric sensor and a photometric circuit that are dedicated for these methods. Such requirement increases the size and cost of the illumination apparatus. Furthermore, the TTL direct metering method cannot be applied to a digital still camera using an imaging device since this method measures the light reflected from a film. Accordingly, it can be said that a method suitable for a digital still camera using an imaging device is the flashmatic method or the pre-illumination method.
One characteristic of the flashmatic method is that photographs can be taken as they appear (white target objects as white, black target objects as black) since the light is emitted in the amount obtained by the above-described formula regardless of the reflectivity of the target object (whether the target object is black or white). On the other hand, in a case where the target object is overall whitish or overall blackish, overexposure or underexposure may occur. Since the measurement error of a distance measurement part serves as the error of the illumination amount, there is a high probability of overexposure or underexposure (including reflectivity of the target object) in a case where the target object having depth is photographed at a close distance.
Meanwhile, in using the pre-illumination method, relatively satisfactory exposure precision can be attained since the illumination amount required for the main photographing process is determined based on the results of measuring the light reflected from the target object in response to the strobe light emitted prior to the main photographing process. Nevertheless, there is a large time lag between activation of the release switch and execution of the main photographing process since the pre-illumination and the calculation of the measured light are performed between the activation of the release switch and execution of the main photographing process. Furthermore, in a case where the illumination apparatus is a strobe type illumination apparatus, the illumination amount of the main photographing process is reduced due to the consumption of charge of the condenser during the pre-illumination process. Thus, the photographing range for long distance becomes smaller.